A. Field of the invention
This invention relates generally to chemical formulations that are used for the preparation of dialysate solutions, and more particularly to the distribution of chemicals into two dialysate concentrate formulations that are particularly suitable for use in preparing dialysate in both batch and proportioning dialysis systems. In the present context, the term “batch” refers to the quantity of dialysate constituents, that when mixed with the proper amount of water, forms enough dialysate solution sufficient for one complete dialysis session for single or multiple patients. The term “proportioning” refers to the traditional types of metering systems that are used to prepare dialysate, namely fixed-volume and dynamic proportioning systems. The two dialysate concentrate formulations are generally suitable for both batch preparation and on-line generation of dialysate as in traditional proportioning metering system after powder concentrate is dissolved to make a liquid concentrate.
B. Statement of Related Art
Kidneys help the body maintain a normal internal environment called homeostasis by ridding the body of excess fluids and metabolic waste products (toxins) as well as maintaining precise levels of glucose and electrolytes. When a person's kidneys fail because of disease or traumatic removal, excess fluid and toxic waste (uremic poisoning) accumulate in that person's body. This uremic poisoning eventually causes death unless the waste material is removed by some artificial means. Dialysis, including hemodialysis and peritoneal dialysis, is a treatment for patients that suffer from kidney failure. In hemodialysis, blood is pumped from the patient's body through an extracorporeal artificial kidney circuit, where blood-borne toxins and excess water are filtered out of the blood through a semipermeable dialyzer membrane into an electrolyte and plasma-resembling medium (i.e., dialysate). In peritoneal dialysis, the patient infuses a quantity of dialysate into the peritoneal cavity, and the peritoneal membrane acts as the semipermeable membrane. After a dwell period, the dialysate fluid is drained and a fresh supply of peritoneal dialysate is added to the peritoneal cavity.
A variety of concentrate formulations for preparing dialysis solutions used in hemodialysis or in peritoneal dialysis are known. See, for instance, U.S. Pat. Nos. 4,336,881; 4,489,535; and 4,756,838. These formulations vary not only with respect to specific constituents, but also with respect to the concentrations of these constituents. Generally, concentrate formulations include sodium chloride as the major constituent and potassium chloride, calcium chloride and magnesium chloride as minor constituents. If required by the patient, dextrose may also be included. Sodium acetate and/or sodium bicarbonate are also included as a buffer source to correct for metabolic acidosis. With acetate buffer, all of the constituents can be combined into a single concentrate. With bicarbonate buffer, two concentrates are necessary to prevent the precipitation of calcium and magnesium as carbonate salts.
Conventional two-part bicarbonate-based dialysis solutions are prepared by mixing an “acid” concentrate, a “base” (i.e., bicarbonate) concentrate and water. Normally the acid concentrate includes all of the acid (e.g., acetic acid), dextrose, calcium, magnesium, potassium and some portion of the physiologic requirement for sodium chloride whereas the base concentrate includes sodium bicarbonate and the balance of the required sodium chloride. In some commercial formulations of dialysate concentrates, the sodium chloride content of the base concentrate is zero. Since acetic acid is a liquid at room temperature, most of the acid concentrates using acetic acid are liquid products; whereas the base concentrates are produced both as powder and liquid concentrates. Many other combinations of acid and base concentrates that are commercially available are specific to the dialysis solution preparation methods and delivery equipment. For instance, the Aksys PHD® dialysis system (available from Aksys, Ltd., Lincolnshire, Ill., USA) uses a liquid acid concentrate and a dry base concentrate housed in two separate vessels. The sequential mixing of the two concentrates with purified water generates carbonic acid as reaction product of the acid with bicarbonate and results in a final dialysate having a pH within physiological limits but with sufficient acidity to prevent calcium and magnesium carbonate precipitation.
As noted above, kidney failure patients accumulate excess fluids and waste products in their body such as blood urea nitrogen (BUN) and creatinine. In fact, the reduction in blood level concentrations of these two substances is generally used to gauge the efficiency and overall effectiveness of dialysis. Often the efficiency of dialysis can be compromised by a number of factors, one of which is the blockage of dialyzer blood flow path by blood clots. Several attempts have been made to prevent or reduce clotting of dialyzer blood flow paths. For instance, Ward et al. U.S. Pat. No. 5,032,615 described the use of extra-corporeal infusion of anti-coagulants during dialysis. Ahmad et al. U.S. Pat. No. 5,252,213, issued Oct. 12, 1993, described the use of anti-coagulants in the dialysate formulations. The methods described in the patents of Ward et al. and Ahmad et al. require complicated monitoring or regulating systems to control the delivery of the anti-coagulants during dialysis or the use of chemical formulations that are inherently unstable and thus cannot be stored for prolonged time periods, respectively.
A number of dialysate delivery systems are available for preparing and delivering dialysate. Traditionally, dialysis systems were used for the preparation of large batches (e.g., 120 L or more) of dialysate. Single batches were prepared by adding dialysate constituents to a batch tank with a predetermined amount of purified water and mixing until dissolution occurred to yield a dialysate having a final desired concentration. A reference describing the preparation of a large quantity of dialysate off-line in 50 liter carboys in a factory-like facility is S. T. Boen et al., Periodic Peritoneal Dialysis Using The Repeated Puncture Technique And An Automatic Cycling Machine, Vol. X Trans. Amer. Soc. Artif. Int. Organs, 44. 409-414 (1964).
The two types of dialysis proportioning systems that are currently used to prepare dialysate include fixed-volume proportioning and dynamic (or servo-controlled) systems. For fixed-volume, proportioning systems, fixed volumes of concentrate and water are mixed to form the final dialysate. Two pumps are used to dispense acid and bicarbonate concentrates while a third pump is used to meter water. The composition of the final dialysate is monitored by a conductivity sensor. Dynamic proportioning systems rely on conductivity monitoring to adjust the amount of acid and base concentrates that is mixed with water to yield a dialysate having a pre-set conductivity. These systems generally employ a second set of conductivity sensors for safety monitoring. The different approaches to preparing bicarbonate-containing dialysate resulted in a variety of proportioning ratios for the acid concentrates, base concentrates and water. Each proportioning ratio requires a particular set of acid and base concentrates. Some dialysis machines are designed for use with a single proportioning ratio while other machines use different proportioning ratios.
With the advent of on-line proportioning systems, dialysates can be prepared continuously on-line by combining water, which has been first purified by a separate water treatment system, with liquid concentrates of the dialysate constituents using a proportioning pump. A representative patent discussing this technique is the patent to Serfass, U.S. Pat. No. 3,441,135. An Association for the Advancement of Medical Instrumentation publication AAMI RD61:2000 describes four such proportioning systems where liquid acid concentrates and liquid bicarbonate concentrates are mixed on line with water to produce a final dialysate for use with hemodialysis therapy. These mix ratios are generally known as 35×, 36.83×, 45× and 36.1×. The details of different proportions are listed in Table 1(b). Recent advancements in automation technology and frequent on-line quality measurements have made it possible for use of proportioning systems in a home setting. New technology have made it possible to overcome the drawbacks of a proportioning systems and offer a more compact design particularly suitable for the home setting.
It is therefore an object of the invention to provide for the improved concentrate formulations of dialysate constituents that are suitable for preparation of batch as well as on-line generation of dialysate. This approach increases the efficiency of dialysis treatment by reducing clotting of blood. It is a further object of the invention to provide dialysate concentrate formulations that are particularly suited for automatic mixing of the constituents in a dialysate or concentrate tank. A further object of the invention is to provide concentrate formulations that assure patient safety, that are storage stable and will withstand temperature extremes when the concentrates are shipped from the location where they are formulated and bottled to the eventual destination.